The refrigerating systems of the present state of the art, which are provided with evaporators with forced ventilation, are controlled by an actuating-transducer device, in the form of a thermostat mounted at a region in the surroundings of the air inlet of the fan, the latter usually being disposed at the region of minimum temperature of the circulating air, i.e., immediately upstream of the evaporator. With the thermostat being so disposed, it simultaneously switches on and off the compressor and the fan, at respective maximum and minimum predetermined temperatures of the air at this region.
The constructions as described above have a yielding and an energy consumption below the optimum possible levels. As soon as the air drawn to the fan reaches its minimum predetermined temperature, deactivating the thermostat and consequently stopping the compressor and the fan, there occurs an air tightness in the circuit. The tightened air will be rapidly heated throughout the circuit, whereas in the surroundings of the evaporator its temperature will fall to unnecessarily low levels, with the low temperature available being not used. The quick temperature increase of the air in the vicinity of the thermostat will cause the frequent actuation of the compressor and fan, with each restart thereof resulting in a corresponding peak of energy consumption.
Moreover, the known refrigerating appliances, particularly refrigerators and freezers, have an undesirable additional heat gain when, during the fan operation, the cabinet door is opened. In such situation, the fan draws the environmental air of higher temperature to the heat exchanging air flow, causing the additional operation of the refrigerating unit.
As evidenced, the available refrigerating appliances present a low thermal yielding, due to the nonutilization of the low temperature of the evaporator, when the fan and compressor are simultaneously switched off, and to the high amount of heat admitted from the outside, when the cabinet door is opened. Said appliances further present a high consumption of electrical energy, due to the frequent operation of the compressor and to the frequent peak currents consumed during the restarts of both the compressor and fan.